You look. It’s there. Then it’s not. Decades go by, and people are prowling the woods, eyes down, hunting for it—crawling, searching, losing hope, and then, all of a sudden, there it is again! In a totally unexpected spot, far from the last sighting, hiding in the dark, barely as tall as your thumb, leafless, probably the rarest plant in Great Britain. It's known as the ghost orchid, and when it shows up, people go nuts.

I’m talking about plant people.

Let the twenty-somethings hunt for Pokemon characters on their smartphones. This is an older game of hide-and-seek—just as obsessive and every bit as crazy.

It starts back in 1855, when a Mrs. Anderson Smith (I see her in a full skirt, edging